Materials for use in making temporary and provisional crowns and bridges, are generally divided into two forms: powder/liquid and paste/paste; two mixing techniques: hand spatulation and automixing; and two curing systems: self-cured and light-cured. Temporary crowns and bridges and provisional crowns and bridges are used pending placement of a permanent crown or bridge in a patients mouth. Those useful for up to three months are often referred to as temporary crowns and bridges while those useful for up to one year are sometimes referred to as provisional crowns and bridges.
The powder/liquid form has been widely used in the past, particularly those containing monofunctional monomers. Typically, the powder component comprises polymers such as poly(methyl methacrylate) mixed with dibenzoyl peroxide. The liquid component comprises plasticizer and monomers such as methyl methacrylate and/or butyl methacrylate. The paste/paste form, developed mainly in the last decade, is usually comprised of multifunctional monomers filled with polymer or glass fillers.
The hand spatulation and mixing technique used in the past has a disadvantage in that it introduce numerous air bubbles into the mixed pastes. The entrapped air bubbles in the hardened material are detrimental to physical strength and lead to sites for bacterial colonies and discoloration. Furthermore, it is very difficult to measure out the proper small quantities needed to mix the components in a desired mixing ratio using this technique.
In very recent years, the automixing technique has become the preferred method for mixing the paste/paste materials. In this technique, the paste materials are individually stored in separate chambers of automix cartridges. When they are to be used, the pastes are automatically mixed and dispensed from their individual chambers and through a static mixer. A static mixer typically has a mixing chamber enclosing a stationary mixing member that causes the individual streams of paste from the cartridge chambers to combine, divide, recombine and mix. Components are extruded from their respective cartridges or cartridge chambers into the mixing chamber in predetermined ratios. The components mix as they pass through the mixing chamber and out an outlet. The ratios are determined by the configurations of the cartridges from which the components are extruded into the mixer.
PROTEMP GARANT by ESPE Dental-Medizin GmbH, Seefeld/Oberbay., Germany, TURBOTEMP by Danville Materials (San Ramon, Calif.) and ULTRA TRIM by Bosworth Co. (Skokie, Ill.) are commercially available cartridges for polymerization mixing in a 1:4 volume ratio of catalyst and base pastes, respectively. LUXATEMP by DMG Hamburg, Germany and INTEGRITY by Dentsply/Caulk (Milford, Del.) are commercially available cartridges for polymerization mixing in a 1:10 volume ratio of catalyst and base pastes, respectively. May et al. in U.S. Pat. No. 5,376,691 discloses two admixable pastes for making temporary crowns and bridges in a volume ratio between 1:5 and 1:20. The U.S. Pat. No. 5,376,691 does not disclose the use of a polymerization inhibitor and contains a polymerizable monomer in the base paste only. Tateosian et al in U.S. Pat. No. 5,554,665 discloses a method and dispenser for making a denture reline. Tateosian employs two pastes of similar viscosities that can be mixed in a volume ratio of 1:1 to 1:5, each past containing a polymerizable monomer and a single polymerization inhibitor such as butylated hydroxytoluene. The entire disclosures of U.S. Pat. Nos. 5,376,691 and 5,554,665 are hereby respectfully incorporated herein by reference.
Prior art temporary crown and bridge materials produced by mixing catalyst and base pastes from a cartridge, in a volume ratio other than 1:1, such as between 1:4 and 1:20, have drawbacks on usage. Most dentists have a delivery system in a 1:1 ratio for dispensing other dental materials, such as impression materials. Dispensing two pastes in ratios other than 1:1 requires a delivery system that is designed in that other desired single predetermined ratio. Therefore, dentists have to either purchase an extra delivery system or change the plunger that is used to push pastes out of the cartridge following the dispensing of an impression material. The first case is not economical and creates the need for added storage space and more time for disinfecting, since there are two systems instead of one. The second case is inconvenient in practice.
It is also typical in prior art methods to mix two liquids or two pastes with the same or similar viscosities in static mixers. The catalyst paste, however, has substantially different Theological characteristics than the base paste. As a result, where the base paste and catalyst paste have the same viscosity, the catalyst paste initially moves through the mixer at a faster rate than the base paste, causing unmixed catalyst paste to appear first at the outlet of the mixer. This causes non-uniform and incomplete curing in portions of the dispensed mixture.
The prior art materials, such as those disclosed in U.S. Pat. No. 5,554,665 produced by mixing two free radical polymerizable acrylic pastes, have a thick oxygen (air) inhibited layer (smear layer) on the surface of the cured materials. An oxygen inhibited layer is a layer of uncured paste in which polymerization is inhibited by oxygen dissolved in the paste from the atmosphere. Such layers cannot be fully avoided in free radical polymerizations. A thick oxygen inhibited layer causes a very sticky surface which creates difficulty in handling and which must be cleaned with alcohol. Furthermore, unreacted monomers in the oxygen inhibited layer may be toxic and cause skin sensitivity.
Ratcliffe et al in U.S. Pat. No. 4,602,076 discloses the use of an organic peroxide in a photopolymerizable dental adhesive composition comprising a ketone photoinitiator that improves cure on irradiation with visible light at ambient temperature and in the presence of air. The U.S. Pat. No. 4,602,076 does not employ polymerization inhibitors.